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The clinical and radiographic results of this very young series of challenging cases are certainly encouraging, even though they did not quite match the performance of resurfacing in primary OA patients performed with first-generation bone preparation and cementing techniques. The difference in survivorship results is accountable to this group presenting greater risk factors, and patient selection should play an important role in the success of the procedure with secondary OA patients. However, changes in the initial surgical technique [31] resulted in a significant improvement in the initial stability and durability of the prosthesis by eliminating the cases of early femoral component loosening. These latter results suggest that a successful resurfacing is possible even with the most challenging cases, and certainly the midterm follow-up review of this series of patients confirms this statement (Fig. 2). However, longer-term follow-up will be important, and we advise patients who have risk factors to avoid impact sporting activities.

The challenge of resurfacing nonprimary OA patients varies with the etiology of each case. Patients with DDH mainly present anatomical challenges (shallow acetabu-lum, greater femoral anteversion and neck-shaft angle, lower offset, and leg length inequalities). Our experience with resurfacing is limited to Crowe class I and II DDH,

Femoral Neck Offset

Fig. 2. A Anteroposterior radiograph of a 47-year-old man with posttraumatic osteonecrosis consecutive to a bicycling accident. The femoral neck fracture was pinned, and the tracks are visible both on the radiograph and in the intraoperative photograph (insert). Note the extensive defects in the femoral head before reconstruction. The additional area for fixation due to the pin tracks may have enhanced the initial fixation. B Nine years after metal-on-metal resurfacing, the patient has resumed a very active lifestyle (including ski racing), and his UCLA hip scores are 10 for pain, walking, and function, and 9 for activity

Fig. 2. A Anteroposterior radiograph of a 47-year-old man with posttraumatic osteonecrosis consecutive to a bicycling accident. The femoral neck fracture was pinned, and the tracks are visible both on the radiograph and in the intraoperative photograph (insert). Note the extensive defects in the femoral head before reconstruction. The additional area for fixation due to the pin tracks may have enhanced the initial fixation. B Nine years after metal-on-metal resurfacing, the patient has resumed a very active lifestyle (including ski racing), and his UCLA hip scores are 10 for pain, walking, and function, and 9 for activity and the results for this etiology were characterized by perfect acetabular initial and enduring component stability, despite incomplete lateral acetabular coverage of the socket (up to 10%-20%), without the need for a special component with adjunct side bar and screw fixation. The rough surface with small porous beads (75-150 |im) provides excellent initial stability when a 1-mm-interference anteroposterior fit is obtained between the anterior and posterior columns. Femoral component durability has been more of a challenge because of failure to provide intimate fixation with good-quality bone, but this problem now appears to be solved with the second-generation surgical technique and cementing of the stem in patients with risk factors.

The technical difficulty of resurfacing patients with LCP disease or SCFE is also related to the anatomical characteristics of these hips. The femoral head is generally flattened, the neck-shaft angle is lower than average, the neck is wide and short, and range of motion is consequently reduced (Fig. 3). Notching of the thicker medial cortex of the femoral neck was sometimes necessary to fit the femoral component when the head-neck ratio approached 1 and the standard-thickness sockets were utilized. However, no femoral neck fractures have been recorded in our series with

Fig. 3. A Anteroposterior radiograph of a 32-year-old man with osteoarthritis (OA) of the left hip secondary to Legg-Calve-Perthes (LCP) disease. Inserts show the Johnson lateral radiograph and the femoral head (above) after preparation. Note the flattening of the head, cystic defects, incongruity with the acetabulum, wide neck with low head-neck ratio, and increased anteversion, which are typical features of LCP with secondary OA. B At 2 years after metal-on-metal Conserve Plus resurfacing using the 3.5-mm acetabular shell. This component allows a gain of 3 mm in femoral head diameter without any extra reaming on the acetabular side as compared to the standard 5-mm shell. There was no need to notch the neck to conserve acetabular bone stock. The component was positioned in a slight posterior-to-anterior position

Fig. 3. A Anteroposterior radiograph of a 32-year-old man with osteoarthritis (OA) of the left hip secondary to Legg-Calve-Perthes (LCP) disease. Inserts show the Johnson lateral radiograph and the femoral head (above) after preparation. Note the flattening of the head, cystic defects, incongruity with the acetabulum, wide neck with low head-neck ratio, and increased anteversion, which are typical features of LCP with secondary OA. B At 2 years after metal-on-metal Conserve Plus resurfacing using the 3.5-mm acetabular shell. This component allows a gain of 3 mm in femoral head diameter without any extra reaming on the acetabular side as compared to the standard 5-mm shell. There was no need to notch the neck to conserve acetabular bone stock. The component was positioned in a slight posterior-to-anterior position this etiology [37]. Notching has not been necessary in more-recent cases utilizing the thin (3.5-mm) shells. In DDH, LCP, and SCFE, 1 mm of leg equalization is generally possible when necessary. Leg lengthening should only be performed by bringing the socket to a more anatomical location and not by leaving the femoral component proud.

Patients with osteonecrosis of the hip present challenges of a different nature. The femoral head often presents with extensive yellowish, friable necrotic bone, which must be completely removed down to the underlying white hard reparative bone to ensure proper component fixation. The residual defects are often large, and these should not be grafted, and the stem should be cemented to maximize the fixation area. Our results highlight that the etiology of osteonecrosis itself does not constitute a contraindication for resurfacing and that the risk factors for the procedure are similar to that of primary OA [16].

Etiologies other than primary OA do not present challenges only to hip resurfacing: numerous reports have shown inferior results when treated with total hip arthroplasty (THA) [38-42] because poor bone quality and hip anatomy also affect conventional reconstructions [43]. In that respect, a prosthetic solution that preserves bone stock on both the acetabular and the femoral sides is particularly indicated for a population of young patients likely to undergo revision surgery within their lifetime. From this perspective, hip resurfacing not only conserves bone at surgery but also preserves bone mineral density of the proximal femur [44-46], another advantage over conventional hip replacement where proximal femoral stress shielding [47,48] can frequently be observed with a decrease in bone mineral density [49-51].

Finally, for hip resurfacing to take its place in the array of conservative solutions for young and active patients, specific training for new surgeons needs to be made available because the procedure is technically more difficult than a conventional THR. Our experience has led to a significant reduction of the complication rate, and minimizing this learning curve for other surgeons is essential for the future success of the procedure, in particular with the most challenging cases.

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